Electrophysiological studies will be performed on thalamic neurons using the in vitro thalamic slice preparation and cells acutely dissociated from such slices. The long-term objectives of these experiments are to further define the electrophysiological properties of different classes of thalamic neurons and the details of their responses to acetylcholine and norepinephrine including the involved receptor types and ionic mechanisms for particular responses. Slow synaptic responses evoked by extracellular stimulation in the dorsal lateral geniculate nucleus and other thalamic sites will be examined in terms of involved transmitters, receptors, and ionic conductances. Patch clamp techniques will be used to examine the low threshold Ca++ current in thalamic neurons. Responses to neurotransmitters in lateral geniculate and intralaminar nuclei will be characterized as will alterations in evoked activities following blockage of GABA/A-mediated IPSPs with convulsant agents. The results of these experiments will be relevant to the general issues of the control of cortical excitability and the development of focal or generalized epileptogenesis.